Human impacts on carbon, nitrogen and phosphorus cycles have differentially increased the flux of C, N and P to the coastal zone creating an altered environment with respect to nutrient stoichiometry for production and transfer of organic matter. Such changes can be more pronounced in closed and semi-enclosed ecosystems. The spatio-temporal variability in chl a, phytoplankton C, N and P content and stoichiometry were measured along with nutrients to reveal relations between them in a coastal lagoon. High nitrate concentrations and low availability of phosphate produced skewed nutrient stoichiometry that reflected itself in the large deviations of PC:PN and PN:PP from their corresponding Redfield ratios while the dynamic nature of fluctuations in nutrient concentrations led to wide variations in phytoplankton C, N and P content and in their ratios. The findings of the study provide insights into the possible alterations in phytoplankton stoichiometry in similar ecosystems receiving high inputs which is not balanced with phosphorus and/or where P-reduction is the mode of eutrophication control as both can produce skewed nutrient stoichiometry.